Earthquakes rapid release of energy = shaking of Earth ... · Earthquakes = shaking of Earth because of a rapid release of energy ... Distribution of earthquakes/ volcanoes along

There are more than 30,000 earthquakes worldwide each year!

● Earthquakes = shaking of Earth because of a rapid release of energy

usually because of movement of tectonic plates

Most earthquakes last for less than a minute.

● Foreshocks = small earthquakes before an earthquake

● Aftershocks = small earthquakes after an earthquake

Earthquakes (cont’d)

● Focus = starting point of the earthquake○ below surface

● Epicenter = point directly above the focus○ on surface

Seismographinstrument that records earthquake waves.

Seismogramprintout of seismic waves

traces of amplified, electronically recorded ground motion made by seismographs

Seismic Waves

Elastic Rebound Hypothesis

1. Rocks are stretched2. Energy accumulates3. Rocks are bent to their

breaking point and vibrate (earthquake)

4. Rocks return to their shape

Momentum MagnitudeDerived from the amount of displacement that occurs along the

fault zone

Locating the Epicenter

1. Use the difference in the arrival times between P & S wave recordings (in minutes).

Distance to the epicenter:

2. Then use the time-travel chart to find the distance (miles or km).

Let’s Practice!

Let’s Practice!

Let’s Practice!

Locating the EpicenterDirection of

the epicenter:

Triangulation:

Once you know the distance to the epicenter, you would need 3 or more seismographs to find the exact location of an earthquake.

Tsunamis

Large sea wave caused when the ocean floor is moves.

Normal beachcondition

Water recedes, so run for your

*@#$ life !!!

Tsunami wave hits,massive flooding

● Fires = often created from broken gas & electrical lines under the city which start a fire.

● Landslides = created when the ground moves downhill from the vibrations.

Lahar: volcanic mudflow of water & ash

Liquefaction: when sandy soil becomes saturated with water and cannot support buildings

San Francisco is built on sandy soil or fill. Many structures built on this type of “soft” soil were badly damaged during the 1989 Loma Prieta earthquake.

Types of Faults

Normal = Hanging Wall moves down & Foot Wall moves up -Tension

Reverse = Foot Wall moves down & Hanging Wall moves up -Compression

Strike-slip = two parts are moving past one another- Shearing

Fun...Hurt??? Footwall Up Normal….Hanging Up Reverse Thrust

IDEA THAT EARTH’S SURFACE IS BROKEN INTO “PLATES” THAT MOVE AROUND

Plate Tectonics

Fault = fracture in the crust where the movement has occurred

Earth’s Structure

Lithosphere = crust & upper mantle; tectonic plates

Asthenosphere = lower mantle & outer core

chemical symbols:Fe = Iron

Ni = Nickel

Plate Tectonics Theorydescribes the formation, movements, & interactions of plates

FUN FACT: = About 95 percent of major earthquakes occur in a few narrow zones near fault lines.

BoundarySec 9.2

Divergent Convergent Transform

Movement:

Structures:

Examples:

BoundarySec 9.2

Divergent Convergent Transform

Movement:

Moving apart

New crust created

Coming together

Crustdestroyed

Plates grind past each other

Crust neither created or destroyed

Structures:

• Oceanic ridge• Rift valleys• Seafloor spreading

• Subduction zone

• Deep Trench• Volcanic activity

Examples:Mid-Atlantic

RidgeAndes

MountainsSan Andreas

Fault

ActionSec 9.3

Ocean – Ocean

Ocean – Continent

Continent - Continent

Convergent:p. 261

Divergent:p. 258

ActionSec 9.3

Ocean – Ocean

Ocean – Continent

Continent - Continent

Convergent:p. 261

Subduction zone, ocean trench, volcanic

island arc

Subduction zone, ocean trench,

volcanoes on continentmountains

Divergent:p. 258

oceanic ridge rift valley

Map of Plate Boundaries

Mechanisms of Plate Movement

1. Mantle convection: movement of heat in the mantle

2. Slab-pull: gravity pulling down on the subducting plate or “slab” & pulling the plate with it

3. Ridge-push: pushing of the plate because of creation of crust at the ridge

Alfred Wegener

● Considered the father of plate tectonics

● Proposed continental drift = Hypothesis that all the continents fit together as one mass, & around 200 million years ago, began to break apart from each other.

● Evidence for Continental Drift:○ Continental Puzzle (Pangaea)○ Matching fossils on different continents○ Matching rock types & mountains on different continents○ Ancient climates

Matching fossils: Matching rock types:

Evidence

● Evidence for Continental Drift:○ Continental Puzzle (Pangaea)○ Matching fossils on different continents○ Matching rock types & mountains on different continents○ Ancient climates

● Evidence for Plate Tectonics:○ Paleomagnetism preserved in seafloor rock layers○ Distribution of earthquakes/ volcanoes along fault lines○ Age of the sea floor rocks/ocean drilling○ Hot spots

Paleomagnetism

● Earth’s magnetic poles switch periodically

● Rocks formed are magnetic → point to magnetic North

● Rocks are found with reverse polarities

rift = new crust formed here

Age of the Sea Floor/Ocean Drilling

● As we move away from ridges, rocks get older

● Radiometric dating of ocean cores

Benthic Foraminifera, Courtesy USGS

Hot Spots

● Plume of magma in the middle of a plate● Hot spot stays when the plate moves & creates islands

examples:•Hawaii•Iceland•Yellowstone